Tennis racquets of metal and other lightweight materials are gaining great popularity over the conventional wooden racquet, which has been known for some time. The conventional wooden racquet has a high torsional resistance and a firmness which gives it a great deal of control of the path of the ball during volley. However, it has a number of disadvantages in that its stiffness causes a great deal of stress on the forearm and elbow area of the player and can result in a malady known as "tennis elbow."
Tennis elbow is believed to be due to irritation of the muscles and tendon tissues in the area of the elbow and forearm. The condition is aggravated by the effort required to move or stop the motion of the racquet and by the shock which is transmitted to the arm on impact of the tennis racquet with a ball. The extreme rigidity of the wooden racquet contributes to transmitting the shock on impact to the arm of the player. Other inherent design factors in the wooden racquet, such as location of the center of percussion near the base of the string area, also contribute to transmitting greater vibration to the player's arm by allowing resonant vibration to be set up along the length of the racquet.
The wooden tennis racquet, due to its solid throat and heavy head and handle areas, has a high wind resistance which slows the stroke of the player somewhat.
The newer metal racquets overcome a number of the deficiencies of the prior art wooden racquet, but do introduce additional problems. The metal racquets have less cross section and more open area, and thus have less wind resistance, which does increase the speed of the player's shot. In addition, the metal racquets are somewhat more flexible, which decreases to some extent the shock which is transmitted to the arm of the player.
The increased flexibility does cause some reduction in control of a shot, particularly on high impact shots, due to the greater angular deflection between the head and handle of the racquet on making a shot. This deflection is both in the direction perpendicular to the face of the racquet in a direction about the hand of the player and also is a twisting action which is apparent when the ball is struck off center. Metal racquets have a high vibrational mode so that a significant shock is transmitted to the player's arm on impact of the ball.
Metal racquets, as well as wooden racquets of prior art, have a high failure due to the stress concentrations that are inherent in the construction of the racquets. Metal racquets are prone to material fatigue in the throat and shoulder areas of the racquet, particularly in the areas where the structures are joined together, either by rivets or welds. Wooden racquets are prone to develop stress-related failure due to the stress concentration caused by string tension and holes in the structure through which the strings pass, as are metal racquets. In addition, wood racquets are prone to warpage due to changes in temperature and humidity.
Application has developed a new composite tennis racquet structure which mitigates the problem of prior art racquets. The structure is also adapted to squash, paddle-ball, badminton, or any other similar batting device. The structure has a light weight, yet can maintain a high moment of inertia, by placing the center of mass farther out toward the tip of the racquet than in previous racquets, and thereby maintaining good shot making properties in the lightweight racquet. The racquet has a good balance between rigidity and flexibility so that control of the shot is not impaired by the racquet, yet less shock is transmitted to the arm of the player on impact of the racquet with the ball. Placement of the center of percussion further toward the tip of the racquet and into the area of normal contact with the ball also contributes the reducing the amount of shock and resonant vibrations which are transmitted through the racquet handle to the arm of the player. The unique composite structure dampens the vibrations which are set up in the racquet on impact so that they are very quickly eliminated and less actual energy is transmitted to the forearm and elbow region of the player.
This damping effect is the result of encasing a metal structural member in a plastic support. The plastic material is continuous from the head to the handle and forms a unitary structure with the metal. The difference in the modulus of elasticity of the two materials and the different vibrational modes of the two materials effectively dampens the vibrations which are set up in the racquet on impact. By using the composite structure of the invention, high strength and very light racquet weight is achieved. Placement of the center of mass and center of percussion can be adjusted further toward the tip of the racquet, if desired, to relocate the center of percussion of the racquet. Relocation of the center of percussion is also facilitated by terminating the metal member at a location spaced from the end of the racquet handle and forming the grip portion as a hollow, molded plastic tube.
In addition, by using this unique composite construction it is possible to eliminate welds, rivets and other stress concentrating structure from the racquet frame, and thereby greatly eliminating failures in the head and throat area of the racquet due to material fatigue. The resulting racquet is both light in weight and strong.